Concept of a Limiting Factor

The concept of a limiting factor was first proposed by Blackman in 1905 as the Law of Limiting Factors. According to this concept, when a biological process depends on several factors, the rate of that process is controlled by the factor that is present in the least favorable amount.

Even if all other conditions are ideal, the overall rate of the process cannot exceed the rate allowed by the most limiting factor. Once that factor is increased to an adequate level, another factor may become limiting.

Limiting Factors of Photosynthesis

Light Intensity

Light provides the energy required for the light reactions of photosynthesis. As light intensity increases, the rate of photosynthesis also increases until a maximum level is reached. Beyond this point, other factors become limiting. Under low light conditions, photosynthesis slows significantly because insufficient energy is available.

Carbon Dioxide Concentration

Carbon dioxide is a raw material used during the Calvin Cycle to produce glucose. When the concentration of CO₂ is low, the rate of photosynthesis decreases because there is insufficient carbon available for fixation. Increasing CO₂ concentration generally increases the rate of photosynthesis until another factor becomes limiting.

Temperature

Photosynthesis is controlled by enzymes, especially during the dark reactions. As temperature increases, enzyme activity also increases, leading to a higher rate of photosynthesis. However, beyond the optimum temperature (usually 25–35°C), enzymes begin to denature and the rate of photosynthesis decreases rapidly.

Water Availability

Water is required for the photolysis process during the light reactions. When water is scarce, plants close their stomata to reduce water loss. This also reduces the entry of carbon dioxide into the leaf, which indirectly limits photosynthesis.